1. Field of the Invention
The invention relates to a hybrid power module, and more particularly, to a hybrid power module of a power amplifier.
2. Description of the Related Art
In amplifier applications, efficiency and linearity are major considerations. For current wireless communication systems, a radio frequency (RF) power amplifier (PA) consumes a majority of the power for portable products. Consequently, a conventional method to extend operation and standby time of wireless communication systems is to improve the efficiency of the power amplifier.
With the spectrum available for radio communication systems becoming more and more limited, this in turn is forcing the development of spectrally-efficient linear modulation schemes. Since the envelopes of a number of these linear modulation schemes fluctuate, the level of the average power, which is being delivered to the antenna, is significantly lower than the level of the maximum power, which results in poor efficiency of the power amplifier.
Linear modulation schemes require linear amplification of the modulated signal in order to minimize undesired out-of-band emissions from spectral re-growth. However, the active devices used within a typical RF amplifying device are inherently non-linear by nature. Only when a small portion of the consumed DC power is transformed into RF power, will the transfer function of the amplifying device be approximated by a straight line, i.e. as in an ideal linear amplifier case. This mode of operation renders the efficiency of the DC to RF power conversion to be low, which is unacceptable for portable (subscriber) wireless communication units.
The emphasis for portable (subscriber) equipment is to increase battery life. To achieve both linearity and efficiency, the so-called linearization techniques are used to improve the linearity of the more efficient amplifier classes.
To help overcome such efficiency and linearity issues, a number of solutions have been proposed. One technique used relates to modulating the power amplifier supply voltage to match the envelope of the radio frequency waveform being transmitted by the RF power amplifier. Envelope modulation requires a feedback signal from the power amplifier supply to one of the control ports of the amplifier. Proposed solutions that utilize envelope modulation include envelope elimination and restoration (EER), and envelope tracking (ET). Both of these approaches require the application of a wideband supply signal to the supply port of the PA.